How to cut crown molding

Coping the inside corner removes material from the underside of the right-hand molding to create a tight fit for an inside corner. Left side molding has a straight-cut end.

If you’ve avoided installing crown molding because of the difficulties involved in creating complex angles at the corners, try this step-by-step approach to take the mystery out of how to cut crown molding.

Tools and materials

In addition to the molding, you’ll need carpenter’s glue, nails and finishing materials, such as caulk and wood putty. Along with the usual hammer, measuring tape, long level and stud finder, you’ll need a miter saw.

If you’re working with a deep molding, the bigger the saw the better – a 12-inch saw is best. If you’re working with moldings deeper than about 7 inches, you’ll need a compound miter saw. Again, a 12-inch sliding compound miter saw would be best.

Coping the end of the right side molding. A pencil mark along the edge gives a distinct line to cut against. This can also be performed with a Dremel-like tool to remove material for a tight fit.

Molding is hand-held, upside down, pressed into the fence and base plate at the angle it will be attached. This molding is narrow enough to be accommodated using a 10-inch saw.

Depending on how you want to handle the inside corners, you might want a coping saw. A coping saw has a large frame and a fine blade.

Or you can use a Dremel-like tool with a cutting wheel. Used with care, a small angle-grinder with the appropriate wheel will also work

A wall protractor is a wise investment as there are no guarantees the walls will meet at an exact right angle. The protractor is essential for walls that meet at any other than a right angle, such as around a bay window, or when the crown molding angles to a cathedral ceiling.

To attach the molding, use a 2-inch brad nailer, preferably cordless electric.

Preparation

Accuracy is key, but not difficult to achieve. Start by drawing layout lines on the walls and ceiling. Place a short length of scrap molding with the top and bottom aligned to both wall and ceiling surfaces, and mark the top and bottom. Move a couple of feet and do it again, then mark a line all around the room by joining these points. This assures the finished molding is tight top and bottom and parallel to the ceiling.

Molding is upside-down and hand-held at the angle it will sit in place (saw fence is tall enough to accommodate this size molding). This will be an outside corner, right hand piece.

While you’re doing this, find the studs and joists and mark their positions on the lines. On runs that are parallel to joists, you may want to make a backing block to fit behind the molding. This is optional but when glued and nailed to studs, it provides a secure nailing point that may make mounting the molding easier.

Carefully measure all the runs of crown molding. You’ll be cutting the molding to fit between walls for inside corners, but longer for outside corners.

Decide whether you want to miter inside corners or cope them. Coping should result in tighter joints, and it disguises out-of-square corners. Practice coping on some short lengths of molding.

You can miter inside corners, if you measure and cut carefully – especially if you’re using jigs. Outside corners are always mitered.

This inside corner has been coped. The left side piece is straight cut at the end, the coped right-side piece fits over the left. The same joint can be made using inside corner cuts on both pieces.

Cutting and installing

If you will be coping corners, cut the first crown molding section with square cuts at each end. Cut it 1/16 to 1/8 inch long so it’s a snug fit. Ideally, you should start with the wall opposite the door. Nail the first piece in place through the top and bottom edges.

If the brads split the molding, you’ll have to pilot drill the nail holes. As a general rule, never nail through any other part of the molding unless you have a backing block in place.

Shown is a completed outside corner. Using some scrap and making the corner will confirm the fit of the corner to the angle of the walls. Always check the angle before setting the miter saw.

Working to the right, the next piece will have a coped inside corner cut at its left end and a square cut at the other. The next piece of molding will be coped with a square cut at the right end. The final piece in a simple room will be coped at both ends.

If the room has outside corners, the crown molding will have to be mitered for an outside corner.

Experts recommend sawing the molding upside down. Think of the bed of the saw as the ceiling and the fence is the wall. You may want to clamp a guide to the saw bed to keep the molding at the correct angle and prevent any twist as you apply pressure with the saw blade.

Clamping a guide to the saw table ensures the shoulder and foot (top and bottom) of the molding are kept in contact with the fence and bed and resist twisting as the saw is lowered.

If it’s hard for you to visualize the direction of the miter, before you cut hold the length of molding up against the first piece and mark the general angle on the surface. This will ensure you set the miter in the correct direction.

Place the molding upside down on the saw with the miter going the direction you rough marked on the set-up. Make the cut, keeping the molding firmly clamped in place with your hand. As always when working with saws, be conscious of safety. Wear safety glasses, pay attention to where the blade will cut, and keep your hands clear of the blade.

Mark the face edge of the cut end using the side of a pencil point, and cope (undercut) the end to the line at about a 30-degree angle. Be very careful not to remove any of the molding face. You may want to finish the coped edge with a file or sandpaper. This step takes care: Try it on some scrap material until you get it right.

To install crown molding without coping, the first piece of molding should be cut with inside corner cuts. The molding will be longer at the bottom and you’ll see material at each end as the facing of the molding is shorter than the back.

Cut the second piece at 90 degrees if goes into a corner and be ready to cope the next run of molding as you did the first.

If the next corner is an outside corner, assemble the coped or mitered second piece and make a mark on the bottom edge at the corner. This will be your cutting mark. Also, make a mark on the ceiling where the top edge falls. This will be the measuring point for the next run. The cut for an outside corner is always mitered and this time the top will be longer than the bottom and the face will be longer than the back side.

Continue with inside and outside corners until you’re back at the start.

An inexpensive jig can be used to obtain the correct cut. In many ways, these are easier to use as it’s possible to visualize the orientation of the cut. The jig also has the orientation marked on top.

This particular jig has an accessory plate to cut 38/52 degree spring angle molding. A bonus is the angled ends to check position of molding as it is nailed.

Cut the second piece at 90 degrees if goes into a corner and be ready to cope the next run of molding as you did the first.

When nailing, start at the joint just completed, then go to the opposite end of the run and check the fit of the next piece, especially if it is an outside corner. If it checks out with a nice tight miter, attach the molding to studs through the bottom end and joists at the top. You can also attach to a backing block if you prefer. You may also want to run a sparing bead of carpenter’s glue along the edges of the molding that contact ceiling and wall to better support and secure the molding.

If the molding is too short for the run of wall, a scarf joint at 45 degrees, one outside, one inside provides an almost undetectable joint, especially when filled and painted.

Finishing details

Use wood putty to fill nail holes. You may also want to run some caulk if the ceiling or walls are not true. You can also squeegee in some caulk at the corners, wiping excess off with a damp sponge.

Using a jig

You can get very acceptable results using a jig to cut crown molding if you find it difficult to visualize the upside-down and inside or outside cutting angles. Jigs can be as inexpensive as $20 or as much as $200. The higher-priced jigs work for different angles and you don’t have to reposition the saw for inside and outside miters. Even the least expensive jig features instructions and marks on the jig to help ensure you make the miter cut in the right direction.

The scarf joint

You can purchase up to 16-foot lengths of crown molding, but you can also join together shorter lengths of molding in a run or combine crown molding for wall span longer than 16 feet using an almost undetectable scarf joint. To create a scarf joint, set the miter saw at 45 degrees and cut the joining pieces left and right at the same angle. One side lies on top of the other and when glued and nailed – preferably over a stud – and then filled and painted, it takes an eagle eye to detect the joint.

–By Steve Sturgess, www.stevesturgess.com